1. Field of the Invention
This invention relates to barrier coatings on paper and especially relates to printing inks that provide a metallic appearance. It further relates to thermal insulation and additionally relates to protective or decorative wrappings and packagings made from paper and plastics to which such inks have been applied.
2. Review of the Prior Art
Metallized papers are useful for many purposes. They provide a less bulky and less expensive paper than foil-laminated paper for many wrapping, covering, and decorative uses where the superb barrier properties of foil-laminated paper are not needed. Holiday and gift wrapping papers, pouch papers, and reflective papers for insulation which do not require the gas-tight barrier properties of foil-laminated papers are examples of such uses.
At the present time, metallized papers and metallized plastics are principally prepared by vacuum deposition of metal onto a moving sheet to form a film varying in thickness from 0.01 mil, or even less, to as much as 3 mils. The metal film conforms exactly to the surface of the paper or plastic base and often must be covered with a protective coating. The metal particles do not bond to each other so that the protective coating must provide whatever barrier properties are needed. Such coatings are applied by processes which are relatively expensive and not readily available to the converter.
Finely divided aluminum particles have long been available as a paste, in order to avoid explosion hazards. Preparation of such pastes is taught, for example, in U.S. Pat. No. 2,144,953 which is directed to pigment pastes consisting essentially of metal flakes, such as 65% aluminum, and a vehicle or thinner comprising stearic acid in solution in an amount equal to about 1% based on metal.
Heat-setting printing inks which are pigmented with metallic powders, so that the inks exhibit unusually effective leafing of the metallic powder on drying and good binding of the metallic powder to the paper, are disclosed in U.S. Pat. No. 3,074,801. As described in Example III, the ink may contain aluminum powder and various thermoplastic resins, such as hydrocarbon resins, which are dissolved in petroleum hydrocarbon with boiling ranges between 450.degree. and 650.degree. F. Such inks are not useful for application in conventional printing operations due to the high boiling points of the solvent component which does not permit drying to a non-tacky state under printing press conditions.
U.S. Pat. No. 3,575,900 is directed to electrostatically sprayable coating solutions containing intimately blended aluminum pigment concentrates which may comprise non-leafing or leafing aluminum pigments dispersed in mineral spirits in combination with a copolymer of vinyl chloride, vinyl acetate, and maleic acid. Again, the drying properties of such solutions do not make them practically applicable to printing operations.
As another approach to forming metallized paper, U.S. Pat. No. 3,463,659 discloses a method for applying a base coat to a sheet by supercalendering, applying a lacquer topcoat, vacuum depositing a metal film (about three millionths of an inch thick) as a metal gas or vapor, and optionally applying a print prime coat thereon. For aluminum, the pressure must be about 0.5 micron in the evaporation area. The dried base coat formulations contain about 52-88% by weight of inorganic coating pigment, about 2-20% by weight of a thermoplastic pigment, about 5-25% by weight of a synthetic emulsion polymer adhesive, and from about 5-25% by weight of a water or alkali-soluble natural polymer adhesive.
There is accordingly a need for a simpler and less expensive process for manufacturing metallized paper and plastics, one in which the base can be directly combined with the metallized coating without requiring base and top coatings, and which is useful with a wide range of papers as the base.